System and method for performing extreme ultraviolet photolithography processes

ABSTRACT

A photolithography system utilizes tin droplets to generate extreme ultraviolet radiation for photolithography. The photolithography system irradiates the droplets with a laser. The droplets become a plasma and emit extreme ultraviolet radiation. The photolithography system senses contamination of a collector mirror by the tin droplets and adjusts the flow of a buffer fluid to reduce the contamination.

BACKGROUND Technical Field

The present disclosure relates to the field of photolithography. Thepresent disclosure relates more particularly to extreme ultravioletphotolithography.

Description of the Related Art

There has been a continuous demand for increasing computing power inelectronic devices including smart phones, tablets, desktop computers,laptop computers and many other kinds of electronic devices. Integratedcircuits provide the computing power for these electronic devices. Oneway to increase computing power in integrated circuits is to increasethe number of transistors and other integrated circuit features that canbe included for a given area of semiconductor substrate.

The features on an integrated circuit die are produced, in part, withthe aid of photolithography. Traditional photolithography techniquesinclude generating a mask outlining the pattern of features to be formedon an integrated circuit die. The photolithography light sourceirradiates the integrated circuit die through the mask. The size of thefeatures that can be produced via photolithography of the integratedcircuit die is limited, in part, on the lower end, by the wavelength oflight produced by the photolithography light source. Smaller wavelengthsof light can produce smaller feature sizes.

Extreme ultraviolet light is used to produce particularly small featuresdue to the relatively short wavelength of extreme ultraviolet light. Forexample, extreme ultraviolet light is typically produced by irradiatingdroplets of selected materials with a laser beam. The energy from thelaser beam causes the droplets to enter a plasma state. In the plasmastate, the droplets emit extreme ultraviolet light. The extremeultraviolet light travels toward a collector with an elliptical orparabolic surface. The collector reflects the extreme ultraviolet lightto a scanner. The scanner illuminates the target with the extremeultraviolet light via a mask.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1A is a side view of a photolithography system, according to oneembodiment.

FIG. 1B is a side view of the photolithography system of FIG. 1A in anoperational state, according to one embodiment.

FIG. 1C is a bottom view of a fluid distributor of the photolithographysystem of FIG. 1A, according to one embodiment.

FIG. 1D is a top view of a portion of the photolithography system ofFIG. 1A, according to one embodiment.

FIG. 2 is a top view of a portion of a photolithography system,according to one embodiment.

FIG. 3A is a side view of a portion of a photolithography system,according to one embodiment.

FIG. 3B is a bottom view of a fluid distributor of the photolithographysystem of FIG. 3A, according to one embodiment.

FIG. 4A is a side view of a photolithography system, according to oneembodiment.

FIG. 4B is a side view of a photolithography system, according to oneembodiment.

FIG. 4c is a top view of the photolithography system of FIG. 4B,according to one embodiment.

FIG. 5 is a block diagram of a control system of a photolithographysystem, according to one embodiment.

FIG. 6 is a block diagram of an analysis model of a control system,according to one embodiment.

FIG. 7 is a flow diagram of a method for operating a photolithographysystem, according to one embodiment.

FIG. 8 is a flow diagram of a method for operating a photolithographysystem, according to one embodiment.

FIG. 9 is a flow diagram of a method for operating a photolithographysystem, according to one embodiment.

FIG. 10 is a flow diagram of a method for operating a photolithographysystem, according to one embodiment.

DETAILED DESCRIPTION

In the following description, many thicknesses and materials aredescribed for various layers and structures within an integrated circuitdie. Specific dimensions and materials are given by way of example forvarious embodiments. Those of skill in the art will recognize, in lightof the present disclosure, that other dimensions and materials can beused in many cases without departing from the scope of the presentdisclosure.

The following disclosure provides many different embodiments, orexamples, for implementing different features of the described subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present description. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various embodiments of thedisclosure. However, one skilled in the art will understand that thedisclosure may be practiced without these specific details. In otherinstances, well-known structures associated with electronic componentsand fabrication techniques have not been described in detail to avoidunnecessarily obscuring the descriptions of the embodiments of thepresent disclosure.

Unless the context requires otherwise, throughout the specification andclaims that follow, the word “comprise” and variations thereof, such as“comprises” and “comprising,” are to be construed in an open, inclusivesense, that is, as “including, but not limited to.”

The use of ordinals such as first, second and third does not necessarilyimply a ranked sense of order, but rather may only distinguish betweenmultiple instances of an act or structure.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. Thus, the appearances of the phrases “in one embodiment” or“in an embodiment” in various places throughout this specification arenot necessarily all referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be combined inany suitable manner in one or more embodiments.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contentclearly dictates otherwise. It should also be noted that the term “or”is generally employed in its sense including “and/or” unless the contentclearly dictates otherwise.

Embodiments of the present disclosure provide many benefits to extremeultraviolet radiation photolithography systems. Embodiments of thepresent disclosure reduce contamination of components of the extremeultraviolet photolithography systems. Embodiments of the presentdisclosure dynamically adjust the flow of a buffer fluid into an extremeultraviolet radiation generation chamber. The buffer fluid helps toprevent and remove contamination of sensitive components of the extremeultraviolet radiation generation chamber. This helps to ensure thatphotolithography processes have adequate extreme ultraviolet radiation.Furthermore, because contamination is removed and prevented, sensitivecomponents of the extreme ultraviolet radiation systems do not have tobe replaced as frequently. The sensitive components can be extremelyexpensive. Accordingly embodiments of the present disclosure not onlyenhance the effectiveness of photolithography processes, but they alsoreduce the cost of operating a photolithography systems becausecomponents need to be replaced less frequently.

FIG. 1A is a side view of an extreme ultraviolet (EUV) photolithographysystem 100, in accordance with one embodiment. FIG. 1A illustrates theEUV photolithography system 100 in a non-operational state. The EUVphotolithography system 100 includes a collector mirror 102 and a shield104. The collector mirror 102 and the shield 104 are coupled together toform an EUV generation chamber 101. EUV light is generated in the EUVgeneration chamber 101. The EUV light is passed from the EUV generationchamber 101 to the scanner 103. The EUV light irradiates aphotolithography target in the scanner 103 via a mask.

In one embodiment, the photolithography system 100 is a laser producedplasma (LPP) EUV radiation photolithography system. The photolithographysystem 100 includes a laser 106, a droplet generator 114, and a dropletreceiver 116. The laser 106, the collector mirror 102, and the dropletgenerator 114 cooperate to generate EUV radiation within the EUVgeneration chamber 101.

As will be described in greater detail in relation to FIG. 1B, thedroplet generator 114 generates and outputs a stream of droplets. Thedroplets can include, in one example, liquid (melted) tin. Othermaterials can be used for the droplets without departing from the scopeof the present disclosure. The droplets move at a high rate of speedtoward the droplet receiver 116. The photolithography system 100utilizes the droplets to degenerate EUV light for photolithographyprocesses. Extreme ultraviolet light typically corresponds to light withwavelengths between 1 nm and 125 nm.

The photolithography system 100 includes a fluid distributor 108. Thefluid distributor 108 includes a plurality of inlets 110 and an outlet112. The fluid distributor 108 includes an inner wall 111 and an outerwall 115. The inner wall 111 and the outer wall 115 define a fluidchamber 113. As will be described in more detail in relation to FIG. 1Band other figures, the fluid distributor 108 receives a buffer fluid atthe inlets 110, the buffer fluid flows through the fluid chamber 113 andis supplied into the EUV generation chamber 101 via the outlet 112. Thebuffer fluid helps to reduce and remove contamination of the collectormirror 102 and the shield 104.

The photolithography system 100 includes a fluid source 118 and massflow controllers 120. The fluid source 118 stores the buffer fluid. Themass flow controllers 120 receive the buffer fluid from the fluid source118 and supply the buffer fluid to the fluid distributor 108. In oneembodiment, each mass flow controller 120 is coupled to a respectiveinlet 110 of the fluid distributor 108 via a respective fluid line 136.Alternatively, the mass flow controllers 120 can be positioned in theinlets 110. The mass flow controllers control the flow rate of thebuffer fluid into the fluid distributor 108.

The photolithography system 100 includes sensors 132. The sensors 132can be positioned external to the EUV generation chamber 101, within theEUV generation chamber 101, or partially within and partially outside ofthe EUV generation chamber 101. The sensors 132 can include lightsensors, electron sensors, plasma sensors, or other kinds of sensors forsensing conditions within the EUV generation chamber 101. Thephotolithography system 100 can include an array of various types ofsensors 132 positioned at various locations within and without the EUVgeneration chamber 101.

The photolithography system 100 includes a control circuit 134. Thecontrol circuit 134 is coupled to the droplet generator 114, a dropletreceiver 116, the laser 106, the fluid source 118, and the mass flowcontrollers 120. The control circuit 134 controls the various componentsof the photolithography system 100. As will be described in more detailbelow, the control system 134 can operate the various components of thephotolithography system 100 to reduce contamination of the reflectorsurface 128 of the collector mirror 102 and the interior surface 130 ofthe shield 104.

FIG. 1B is an illustration of the photolithography system 100 of FIG. 1Ain an operational state, according to one embodiment. In the operationalstate, the droplet generator 114 generates and outputs a stream ofdroplets 140. The droplets can include tin, though droplets of othermaterial can be utilized without departing from the scope of the presentdisclosure. The droplets 140 move at a high rate of speed toward thedroplet receiver 116.

In one embodiment, the droplet generator 114 generates between 40,000and 100,000 droplets per second. The droplets 140 have an initialvelocity of between 60 m/s to 200 m/s. The droplets have a diameterbetween 10 μm and 200 μm. The droplet generator 114 can generatedifferent numbers of droplets per second than described above withoutdeparting from the scope of the present disclosure. The dropletgenerator 114 can also generate droplets having different initialvelocities and diameters than those described above without departingfrom the scope of the present disclosure.

The laser 106 is positioned behind the collector mirror 102. Duringoperation, the laser 106 outputs pulses of laser light 142. The pulsesof laser light 142 are focused on a point through which the dropletspass on their way from the droplet generator 114 to the droplet receiver116. Each pulse of laser light 142 is received by a droplet 140. Whenthe droplet 140 receives the pulse of laser light 142, the energy fromthe laser pulse generates a high-energy plasma from the droplet 140. Thehigh-energy plasma outputs EUV radiation.

In one embodiment, the laser 106 is a carbon dioxide (CO₂) laser. TheCO₂ laser emits radiation or laser light 142 with a wavelength centeredaround 9.4 μm or 10.6 μm. The laser 106 can include lasers other thancarbon dioxide lasers and can output radiation with other wavelengthsthan those described above without departing from the scope of thepresent disclosure.

In one embodiment, the laser 106 irradiates each droplet 140 with twopulses. A first pulse causes the droplet 140 to flatten into a disk likeshape. The second pulse causes the droplet 140 to form a hightemperature plasma. The second pulse is significantly more powerful thanthe first pulse. The laser 106 and the droplet generator 114 arecalibrated so that the laser 106 emits pairs of pulses such that eachdroplet 140 is irradiated with a pair of pulses. For example, if thedroplet generator 114 outputs 50,000 droplets per second, the laser 106will output 50,000 pairs of pulses per second. The laser 106 canirradiate droplets 140 in a manner other than described above withoutdeparting from the scope of the present disclosure. For example, thelaser 106 may irradiate each droplet 140 with a single pulse or withmore pulses than two. Moreover, the primary laser here can not onlycause droplets to flatten into disk-like shape can be mist or vaporstate.

In one embodiment, the droplets 140 are tin. When the tin droplets 140are converted to a plasma, the tin droplets 140 output EUV radiation 146with a wavelength centered between 10 nm and 15 nm. More particularly,in one embodiment, the tin plasma emits EUV radiation with a centralwavelength of 13.5 nm. These wavelengths correspond to EUV radiation.Materials other than tin can be used for the droplets 140 withoutdeparting from the scope of the present disclosure. Such other materialsmay generate EUV radiation with wavelengths other than those describedabove without departing from the scope of the present disclosure.

In one embodiment, the radiation 146 output by the droplets scattersrandomly in many directions. The photolithography system 100 utilizesthe collector mirror 102 to collect the scattered EUV radiation 146 fromthe plasma and output the EUV radiation toward a photolithographytarget.

In one embodiment, the collector mirror 102 is a parabolic or ellipticalmirror. The scattered radiation 146 is collected and reflected by theparabolic or elliptical mirror with a trajectory toward the scanner 103.The scanner 103 utilizes a series of optical conditioning devices suchas mirrors and lenses to direct the EUV radiation to thephotolithography mask. The EUV radiation 146 reflects off of the maskonto a photolithography target. The EUV radiation 146 reflected from themask patterns a photoresist or other material on a semiconductor wafer.For purposes of the present disclosure, particularities of the mask andthe various configurations of optical equipment in the scanner 103 arenot shown.

In one embodiment, the collector mirror 102 includes a central aperture126. The pulses of laser light 142 pass from the laser 106 through thecentral aperture 126 toward the stream of droplets 140. This enables thecollector mirror 102 to be positioned between the laser 106 and thephotolithography target.

Because the droplets 140 traveled a high rate of speed are either in aliquid or plasma state, when the droplets 140 are received into thedroplet receiver 116, there may be a splash effect. It is possible thatsome splash back may occur. The splash back may result in material fromthe droplets 140 landing on the reflective surface 128 of the collectormirror 102 or on the interior surface 130 of the shield 104.Additionally, it is possible that when the droplets 140 are irradiatedwith laser light 142, that some plasma vapor may be generated. Theplasma vapor 140 may eventually deposit on the surface 128 of thecollector mirror 102 and on the interior surface 130 of the shield 104.

The accumulation of material from the droplets 140 on the surface 128 ofthe mirror 102 and on the interior surface 103 of the shield 104 mayresult in poor performance of the photolithography system 100. Forexample, the photolithography system 100 depends on a sufficient amountof EUV light 146 being reflected from the collector mirror 102 into thescanner 103. If an insufficient amount of EUV light 146 is reflectedfrom the collector mirror 102 into the scanner 103, then thephotolithography system 100 may not be able to properly perform aphotolithography process. When material from the droplets 140accumulates on the reflective surface 128 of the collector mirror 102,then the reflectivity of the reflective surface 128 is reduced. This canresult in an insufficient amount of EUV light 146 being provided to thescanner 103. Furthermore, accumulation of material on the interiorsurface 130 of the shield 104 can also have an adverse impact on theperformance of the photolithography system 100.

The photolithography system 100 implements the fluid distributor 108 inorder to reduce the accumulation of material from the droplets 140 onthe surface 128 of the mirror 102 and on the interior surface 130 of theshield 104. The fluid distributor 108 distributes a buffer fluid 148into the EUV generation chamber 101. The buffer fluid 148 is selected toremove accumulated droplet material from the surface 128 of the mirror102 and the interior surface 130 of the shield 104. The buffer fluid 148is also selected to inhibit material from the droplets 140 fromaccumulating on the reflective surface 128 and on the interior surface130.

In one embodiment, the droplets 140 are tin and the buffer fluid 148 isa hydrogen gas. The hydrogen gas can include H2. The hydrogen gas reactswith the tin and etches accumulated tin material from the surfaces 128and 130. Accordingly, one effect of the hydrogen buffer fluid is tochemically react with the tin in order to remove the tin from thesurfaces 128 and 130. Another effect of the hydrogen buffer fluid 148 isto physically carry tin material away from the surfaces 128 and 130. Inother words, the flow of the hydrogen buffer fluid 148 can physicallycarry tin material away from the surfaces 128 and 130. One example hasbeen given in which the droplets 140 are tin in the buffer fluid 148 ishydrogen gas, other materials from the droplets 140 and other bufferfluids 148 can be used without departing from the scope of the presentdisclosure.

One challenge associated with reducing the accumulation of material onthe surfaces 128 and 130 is the uneven flow of the buffer fluid 148along the various regions of the surfaces 128 and 130. If the bufferfluid 148 does not flow along all areas of the surfaces 128 and 130,then it is possible that material from the droplets 140 may accumulateat these regions of buffer fluid flow.

In order to promote sufficient flow of the buffer fluid 140 along allareas of the surfaces 128 and 130, the fluid distributor 108 includes aplurality of inlets 110. In particular, the fluid distributor 108includes four or more inlets 110. The inlets 110 can be positionedevenly along the lower surface of the fluid distributor 108. The largenumber of inlets 110 and the even spacing of the large number of inlets110 can result in a more even flow of the buffer fluid 148 at allpositions of the outlet 112. This dynamic may be better understood withreference to FIGS. 1C and 1D.

FIG. 1C is a bottom view of the fluid distributor 108 of FIGS. 1A and1B, according to one embodiment. In the example of FIG. 1C, the fluiddistributor 108 includes eight inlets 110. The eight inlets 110 eachreceive a flow of the buffer fluid 148 from a respective fluid line 136(not shown in FIG. 1C). The fluid or sugar 108 includes a solid bottomsurface 117. The solid bottom surface 117 prevents flow of fluid intothe fluid chamber 113 of the fluid distributor 108 except through theinlets 110. Other numbers and shapes of inlets 110 can be utilizedwithout departing from the scope of the present disclosure. In order topromote uniform coverage of gas flow on the various regions of thesurfaces 128 and 130, it can be beneficial to have a number of inlets110 that enables symmetrical positioning of the inlets 110.

FIG. 1D is a top view of a portion of the fluid distributor 108 and thecollector mirror 102 of FIG. 1A, according to one embodiment. In theexample of FIG. 1D, the top of the fluid distributor 108 is entirelyopen between the inner wall 111 and the outer wall 115. In other words,the top of the fluid distributor 108 corresponds to a single continuousoutlet 112 that enables the buffer fluid 148 to flow from the fluidchamber 113 into the EUV generation chamber 101. Other configurations ofa fluid distributor 108 can be utilized without departing from the scopeof the present disclosure. For example, the fluid distributor 108 mayinclude a plurality of individual outlets 112 separated from each otherby a solid top surface. The top view of FIG. 1D also illustrates thedroplet generator 114 and the droplet receiver 116. The top view of FIG.1B does not illustrate the shield 104.

The buffer fluid 148 flows into the fluid chamber 113 of the fluiddistributor 108 via the inlets 110. The buffer fluid 148 flows from thefluid chamber 138 into the EUV generation chamber 101 via the continuousoutlet 112. This configuration promotes substantial flow of the bufferfluid 148 along all regions of the surfaces 128 and 130

In one embodiment, the flow of the buffer fluid 148 from the fluidsource 118 into each fluid line 136 may be controlled by a respectivemass flow controller 120. Each mass flow controller 120 can beselectively operated to provide a selected flow of the buffer fluid 148into the respective inlet 110 via the corresponding fluid line 136. Inone embodiment, the mass flow controllers 120 are each positioned withina respective inlet 110. In this case, the fluid lines 136 deliver fluidfrom the fluid source 118 to the inlets 110. The mass flow controllers120 control the flow rate of the buffer fluid 148 into the fluid chamber113.

FIG. 2 is a top view of a portion of a photolithography system 200,according to one embodiment. The photolithography system 200 issubstantially similar to the photolithography system 100 of FIGS. 1A-1D,except that the fluid distributor 108 includes multiple mutuallyexclusive fluid chambers 113. The mutually exclusive fluid chambers 113are defined by internal partitions 150. The internal partitions 150extend from the bottom surface 117 (see FIG. 1C) of the fluiddistributor 108 to a top of the fluid distributor 108. Each fluidchamber 113 receives the buffer fluid 148 through a respective inlet110. The inlets 110 are shown in dashed lines.

The fluid distributor 108 of FIG. 2 includes a plurality of outlets 112.Each outlet 112 extends between two of the internal partitions 150.Accordingly, each fluid chamber 113 outputs the buffer fluid 148 througha respective outlet 112.

In one embodiment, the fluid distributor 108 of FIG. 2 enables enhancedcontrol of buffer fluid flow from particular regions of the fluiddistributor 108. As will be set forth in more detail below, the controlcircuit 134 may determine that flow rates of the buffer fluid 148 shouldvary at different output regions of the fluid distributor 108. In thiscase, the control system 134 can selectively control the various massflow controllers 120 can provide varying flow rates of the buffer fluid148 into the individual fluid chambers 113 via the inlets 110. Becausethe fluid chambers 113 are separated from each other by the internalpartitions 150, selectively controlling the mass flow controllers 120enables selectively controlling the flow of the buffer fluid 148 fromvarious parts of the fluid distributor 148.

FIG. 3A is an enlarged sectional view of a portion of a photolithographysystem 300, according to one embodiment. The photolithography system 300can be substantially similar to the photolithography system 100 of FIGS.1A-1D, except that the fluid distributor 108 of the photolithographysystem 300 includes some additional features with respect to the fluiddistributor 108 of FIGS. 1A-1D. In particular, the fluid distributor 108includes an internal partition 180. The internal partition 180 separatesa first fluid chamber 113 a from a second fluid chamber 113 b within thefluid distributor 108. The disposition of the internal partition 180 canbe more fully understood with reference to FIG. 3B.

FIG. 3B is a bottom view of the fluid distributor 108 of FIG. 3A,according to one embodiment. FIG. 3B illustrates that the internalpartition 180 separates a plurality of inlets 110 a from a plurality ofinlets 110 b. Furthermore, the partition 180 is shown in dashed lineswhere the partition 180 is covered from view by the bottom surface 117of the fluid distributor 108. Accordingly, in one embodiment, theinternal partition 180 extends in a circle between the inner wall 111and the outer world wall 115. Though not illustrated in FIG. 3A, thefluid distributor 108 can also include internal partitions 150 as shownin FIG. 2.

Returning to FIG. 3A, a mass flow controller 120 a is positioned in theinlet 110 a. A mass flow controller 120 b is positioned in the inlet 110b. Each inlet 110 a can include a mass flow controller 120 a. Each inlet110 b can include a mass flow controller 120 b. In an example in whichthe internal partitions 150 are not present, there is a singlecontinuous first fluid chamber 113 a and the single continuous secondfluid chamber 113 b. Each of the inlets 110 a, with the mass flowcontrollers 120 a, provides the buffer fluid 148 into the first fluidchamber 113 a. Each of the inlets 110 b, with the mass flow controllers120 b, provides the buffer fluid 148 into the second fluid chamber 113b. As will be described in more detail below, the mass flow controllers110 a, 110 b can be selectively operated to provide varying flow ratesof the buffer fluid 148 into the first and second fluid chambers 113 a,113 b. Each of the inlets 110 a, 110 b can receive the buffer fluid 148from respective fluid lines 136 (not shown). In some embodiments, themass flow controllers 120 a, 120 b are positioned external to the inlets110 a, 110 b. The fluid distributor 108 includes a first outlet 112 athat provides the buffer fluid 148 from the first fluid chamber 113 ainto the EUV generation chamber 101. The fluid distributor 108 includesa second outlet 112 b that provides the buffer fluid 148 from the secondfluid chamber 113 b into the EUV generation chamber 101.

The photolithography system 300 includes a director vane 156. Thedirector vane 156 is rotatably coupled to a joint 154. The director vane156 can rotate through various positions via the joint 154. The directorvane 156 can help direct buffer fluid 148 along the surface 130 of theshield 104 and the surface 128 of the collector mirror 102. As will bedescribed in more detail below, the control system 134 can control theposition of the director vane 156. Accordingly, the director vane 156can selectively affect the flow of the buffer fluid 148 from the outlets112 a, 112 b.

Though not shown in FIG. 3A, the photolithography system 300 can includea plurality of director vanes 156 positioned around the top of the fluiddistributor 108. Each of the vanes 156 can be selectively controlled todirect the flow of buffer fluid 148. In an example in which the internalpartitions 150 are present, there may be a plurality of first fluidchambers 113 a and second fluid chambers 113 b, and corresponding firstoutlets 112 a and second outlets 112 b. There may be a respectivedirector vane 156 for each pair of first and second outlets 112 a, 112b. The director vanes 156 may have a width corresponding to the distancebetween internal partitions 150.

FIG. 4 is an illustration of a photolithography system 400, according toone embodiment. The photolithography system 400 is substantially similarto the photolithography system 100 of FIGS. 1A-1D, except that thephotolithography system 400 includes the particular array of lightsensors 162 and charge coupled devices 160. Though not shown in FIG. 4,the photolithography system 400 also includes the droplet generator 114and the droplet receiver 116.

In one embodiment, the light sensors 162 are positioned to detect sidescattering of EUV radiation from the plasmatized droplets 140. The lightsensors 162 can be part of a side scatter detection system 116 asdescribed in relation to FIG. 1.

In one embodiment, the light sensors 162 collectively detect a currentlevel of intensity of EUV light being generated in the EUV generationchamber 101. A plurality of light sensors 162 can be positionedlaterally around the outside of the shield 104 at various heights. Theplurality of light sensors 162 are configured to sense EUV light. Thelight sensors 160 to provide sensor signals to the control system 134.The control system 134 can analyze the sensor signals from the lightsensors 162 to determine the reflectivity of various regions of thesurface 128 of the collector mirror 102 and the surface 130 of theshield 104. As will be set forth in more detail below, the controlsystem 134 can utilize these determinations to selectively increase theflow of the buffer fluid 148 to regions of the surface 128 and thesurface 130 on which are accumulated matter from the droplets 140. Thecontrol system 134 can control the mass flow controllers 120, thedirector vanes 156, and other aspects of the photolithography system 400in order to remove accumulated droplet material from the surfaces 128and 130.

In one embodiment, the light sensors 162 are utilized to detect Thomsonscattering of EUV radiation from the plasmatized droplets. The Thomsonscattering phenomenon is due to elastic scattering of electromagneticradiation by a single free charged particle. This can be utilized as ahigh temperature plasma diagnostic technique. In particular, Thomsonscattering measurements can be utilized to determine the ionization ratein the droplets. The intensity of scattered light is based, in part, onthe extent of the laser to plasma interaction. Accordingly, theionization rate can be retrieved from the intensity of scattered light.Thomson scattering intensity is independent of incident lightwavelength. Thus, Thomson scattering can be useful to analyze therelationship between the electric field of incident light and electrondensity. The light sensors 162 generate signals indicative of theintensity of side scattered light and pass the signals to the controlsystem 134.

In one embodiment, the light received by the light sensors 162 can beutilized to determine a shape of the droplets 140 after being impactedby a first pulse of laser light 142 and the second pulse of laser light144. In general, the first pulse of laser light flattens the receivingdroplet 140 into a pancake shape. The pancake shaped droplet 140 can betilted at various angles relative to the direction of travel of thedroplets 140. The pancake shape angle of the droplet 140 can result inaccumulation of droplet matter in particular locations on the surface128 in the surface 130. Accordingly, the control system 134 can analyzethe light received by the light sensors 162 to determine the shape andangle of the droplet 140 after being impacted by the first pulse oflaser light 142 and after being impacted by the second pulse of laserlight 142.

The total intensity of EUV light emitted by plasma can be estimated orcalculated based on the amount of light received by the light sensors162. On average, the plasma will emit EUV light at the same rate in alldirections, or with known relationships between various scatteringdirections. Accordingly, the total intensity of EUV light can beestimated or calculated based on the light received by the light sensors162.

In one embodiment, the light sensors 162 can be utilized to detectcontamination of the surface 128 of the collector 102. The reflectivityof the surface 102 will be reduced at contaminated areas. Accordingly, asubset of the light sensors 162 and/or other light sensors positioned inthe scanner can be utilized to determine the reflectivity each of aplurality of areas on the surface 128 of the collector 102. The lightsensor information can be utilized to generate a contamination map. Thecontamination map indicates the contamination level of each area of thesurface 128. The control system 134 can generate the contamination mapbased on sensor signals received from the light sensors 162 and/or othersensors.

In one embodiment, the control system can adjust buffer fluid flowparameters to provide increased buffer fluid flow to those regions ofthe surface 128 that are more heavily contaminated. The control system134 can selectively control the mass flow controllers 110 and thedirector vanes 156 to increase or decrease the flow of the buffer fluidonto the various areas of the surface 128 based on the contaminationmap.

In one embodiment, the photolithography system 400 includes a pluralityof lenses 164. Each lens 164 is positioned to focus light scattered fromthe plasmatized droplets 140 onto or into the light sensors 162. Thoughthe lenses 164 are shown as being positioned external to the EUVgeneration chamber 101, in practice, the lenses 164 may be positioned inother locations or orientations than those shown in FIG. 4.

In one embodiment, the one or more lenses 164 are coupled to a rim ofthe collector mirror 102. The lenses 164 can be positioned in a samelateral plane as the droplet generator 114 and droplet receiver 116.Side scattered light from the plasma droplets passes through theselenses 164 and is focused onto the light sensors 162.

In one embodiment, the one or more lenses 164 can correspond to windowsin the shield 104 of the EUV generation chamber 101. Accordingly, ashield 104 of the EUV generation chamber 101 can include windows orapertures. Lenses 164, or lensing materials, can be positioned in thewindows or apertures. When light is scattered from the plasma, the lightpasses through the windows and onto the light sensors. The lenses 164positioned in the windows or apertures can focus the light onto thelight sensors 162.

In one embodiment, the light sensors 162 provide sensor signals to thecontrol system 134. The sensor signals are indicative of the intensityof light received by the light sensors 162. The control system 134receives the sensor signals and can adjust parameters of thephotolithography system 400 responsive to the sensor signals.

In one embodiment, the control system 134 adjust parameters of thephotolithography system 400 in order to more effectively prevent andremove accumulations of droplet matter on the surfaces 128 and 130. Inone embodiment, the control system 134 adjusts parameters of thephotolithography system 400 in order to more effectively generate EUVradiation. The control system 134 can adjust one or more of buffer fluidflow rates into various inlets 110, the positions of director vanes 156,droplet speed, droplet size, laser pulse power, laser pulse timing,laser pulse train profile, initial droplet temperature, pressure withinthe EUV generation chamber, or other parameters.

In one embodiment, adjusting aspects of the laser pulses can includeadjusting the plasma generation pulse that generates the plasma from theflattened droplet 140. The plasma generation pulse is utilized togenerate a plasma from the flattened droplet. The timing, pulse shape,and power of the plasma generation pulse can be adjusted by the controlsystem 134 responsive to the sensor signals from the light sensors 162.

In one embodiment, the photolithography system includes charged particledetectors 160. The process of generating a plasma results in thegeneration of charged particles in the droplets 140. Some of the chargedparticles may be ejected from or may otherwise travel away from thedroplets. The characteristics of the charged particles ejected from theplasma are indicative of characteristics of the plasma itself. Thecharacteristics of the charged particles can include velocity of thecharged particles, the energy of the charged particles, the trajectoryof the charged particles, the number of charged particles emitted perdroplet, and other characteristics.

In one embodiment, the charged particle detectors 160 are coupled to thecontrol system 134. The charged particle detectors 160 are configured togenerate sensor signals indicative of parameters of the chargedparticles. The charged particle detectors 160 pass the sensor signals tothe control system 134.

In one embodiment, an array of charged particle detectors 160 ispositioned within the EUV generation chamber 101. The array of chargedparticle detectors 160 can be positioned to detect a variety of chargedparticle trajectories within the EUV generation chamber 101. In otherwords, the charged particle detectors 160 can be positioned in variouslocations throughout the EUV generation chamber 101. Each of the chargedparticle detectors 160 detects impacts of charged particles on thecharged particle detectors 160. The charged particle detectors 160 passsensor signals indicative of characteristics of the charged particles tothe control system 134.

FIG. 4A illustrates the charged particle detectors 160 as beingpositioned on an exterior wall of the EUV generation chamber 101.However, the charged particle detectors 160 can be positioned within theEUV generation chamber 101. For example, the charged particle detectors160 can be positioned on the interior surface 130 of the shield 104 ofthe EUV generation chamber 101. Alternatively, the charged particledetectors 160 can be positioned, supported, or arranged in other ways inan interior or an exterior of the EUV generation chamber 101. In oneembodiment, the EUV generation chamber 101 can include apertures thatpermit charged particles to pass from an interior of the EUV generationchamber 101 to the charged particle detectors 160. In one embodiment,may include charged particle lenses that direct charged particles intothe charged particle detectors 160 via electromagnetic forces.

In one embodiment, the charged particle detectors 160 include chargecoupled devices configured to detect impacts from charged particles. Thecharge coupled devices generate signals each time a charged particleimpacts the charge coupled devices. The charge coupled devices then passsensor signals to the control system 134.

In one embodiment, the charge coupled devices for detecting chargedparticles include electron multiplying charge coupled devices. Theelectron multiplying charge coupled devices are frame transfer chargecoupled devices that include an output register. The electronmultiplying charge coupled device can include a fluorescent film orsheet positioned in front of a sensor area of the charge coupled device.When charged particles impact the florescent film, the florescent filmemits light. The light is sensed by the charge coupled device and thecharge coupled device counts the impact of the charged particle.

In one embodiment, the charged particle detectors can include Faradaycups. A Faraday cup is a conductive cup that is configured to detect orcapture charged particles in a vacuum, such as a vacuum in the EUVgeneration chamber 101. The Faraday cup generates a current based on thecharged particles captured by the Faraday cup. This current can beutilized to determine the number of charged particles that impact thecup. The Faraday cups can provide sensor signals to the control system134 indicative of the number of charged particles collected or capturedby the Faraday cups.

In one embodiment, the control system 134 can adjust parameters of thephotolithography system 100 responsive to the sensor signals from thecharged particle detectors 160. The control system 134 can adjust thesame sorts of parameters of the photolithography system 400 as thosedescribed previously in relation to the light sensors 162. The controlsystem 134 can adjust the parameters of the photolithography system 200in order to more effectively generate EUV radiation for performingphotolithography.

In one embodiment, the control system 134 can generate a 3D model of thedroplets 140 after the flattening pulse and/or the plasma generationpulse. Because the charged particle detectors 160 are positioned invarious locations throughout the EUV generation chamber 101 and/or thescanner 103, the sensor signals from the various charged particledetectors can be utilized to generate a 3D model of the droplets priorto injection of the charged particles. The 3D model can indicate a shapeof the flattened droplets after the flattening pulse and before theplasma generation pulse. Alternatively, or additionally, the 3D modelcan indicate a shape of the flattened droplets after the plasmageneration pulse. The control system 134 can analyze the 3D model inorder to determine whether the flattening pulse, the plasma generationpulse, the droplet speed, droplet size, the initial droplet temperature,or other parameters should be adjusted in order to generate a plasmahaving a selected shape from the droplets. The 3D model can help predictwhere droplet material will accumulate on the surfaces 128 and 130.Accordingly, the control system 134 can utilize the 3D model todetermine how to direct the flow of the buffer fluid 148.

In one embodiment, the control system 134 can adjust parameters of thephotolithography system 400 responsive to sensor signals from the lightsensors 162 and the charged particle detectors 160. The control system134 can generate a model of the flattened droplets 140, the plasmatizeddroplets 140, or of other aspects of the plasma or droplets 140 based onthe combination of sensor signals from both the light sensors 162 andthe charged particle sensors 130, 136.

In one embodiment, the control system 134 utilizes machine learning toaccurately adjust the parameters of the photolithography system 400 inorder to avoid, reduce, or remove the accumulation of droplet matter onthe surfaces 128 and 130. Accordingly, the control system 134 caninclude a machine learning model that can be trained to adjust one ormore parameters of buffer fluid flow, the laser pulses, or droplets 140responsive to sensor signals received from the light sensors 162 and/orthe charged particle detectors 160.

In one embodiment, the machine learning model includes a neural network.The machine learning model can include one or more neural network-basedsupervised machine learning models. The machine learning model caninclude one or more unsupervised machine learning models. Other types ofmachine learning models can be utilized for controlling the speed ofdroplets without departing from the scope of the present disclosure. Forexample, machine learning models other than neural network-based machinelearning models can be utilized by the control system 134.

The image generated from electron multiplying type charge coupleddevices may need post processing due to different electron energies withdifferent deflective directions. The image can include energy(distribution on image) and counts (intensity on image) information.Therefore, to recover an XY plane image to resolve originaldistribution, corrections may be made. By known optics specification,the position in a volume with a particular geometry can be estimated.

In one embodiment, by recording the information from Thomson scatteringphenomenon and electron distribution in space, the original electrondensity distribution from the plasma could be computed in multipledimensions. From Thomson scattering theory, the relation betweenincident light intensity and the electron density distribution can alsobe retrieved. By analyzing the relation of electrons distribution inspace and combining the results in three dimensions, the control system134 can compose a 3D plasma model.

In one example, the X-Y distribution of the plasma can be calculatedbased on side-scattered light information. The side scattered lightinformation can be collected by light sensors 162 positioned near thecollector mirror. The Z distribution of the plasma can be calculatedbased on the charged particle data sensed by the charged particlesensors 160 further away from the collector 102 in the verticaldirection. Some of the charged particle sensors 160 may be positioned inthe scanner or near the scanner. The 3D model may correspond tocalculating the X-Y and Z distribution of the plasma, based on theseparameters. The 3D model indicates the quality of the plasma.Accordingly, the control system 134 can generate the 3D plasma modelbased on sensor signals from the light sensors 162 and the chargedparticle sensors 160. The 3D models can be utilized to assist inidentifying adjustments to the prepulse laser, the plasmatizing laser,and the droplets.

FIG. 4B is an illustration of the EUV photolithography system 400 ofFIG. 4A and including a plasmatized droplet 140. The plasmatized droplet140 has been plasmatized after receiving the plasma laser pulse from thelaser 106. Plasmatized droplet 140 is flattened. The flattened dropletmay be called a plasma pancake. The flattened droplet 140 is tilted atan angle Theta with respect to horizontal. The angle of the flatteneddroplet 140 can affect the location of accumulated contamination 171 onthe surface 128 of the collector 102. The 3D model of the plasmadescribed previously indicates the tilt angle Theta. Accordingly, the 3Dmodel can be utilized to predict the location of accumulation ofcontamination 171.

FIG. 4C is a top view of the EUV photolithography system 400, accordingto one embodiment. The top view of FIG. 4C illustrates that the lightsensors 162 and the lenses 164 are positioned radially around thecollector 102. Though not shown in FIG. 4C, the on the surface chargedparticle detectors 160 may also be radially arranged. FIG. 4C alsoillustrates the plasmatized droplet 140 of FIG. 4B. The 3D modeldescribed previously can indicate the shape of the droplet 140 in thehorizontal plane as seen from the top view of FIG. 4C. FIG. 4C alsoshows the accumulated contamination 171 on the surface 128 of thecollector 102.

FIG. 5 is a block diagram of the control system 134, according to oneembodiment. The control system 134 of FIG. 5 is configured to controloperation of a EUV photolithography system, according to one embodiment.The control system 134 utilizes machine learning to predict dropletmatter accumulation based on the plasma generation parameters and thebuffer fluid flow parameters.

In one embodiment, the control system 134 includes an analysis model 180and a training module 170. The training module trains the analysis model180 with a machine learning process. The machine learning process trainsthe analysis model 180 to predict droplet matter accumulation based onEUV system parameters including buffer fluid flow parameters and EUVgeneration parameters. Although the training module 170 is shown asbeing separate from the analysis model 180, in practice, the trainingmodule 170 may be part of the analysis model 180.

The control system 134 includes, or stores, training set data 172. Thetraining set data 172 includes historical EUV system parameters data 174and contamination data 176. The historical EUV system parameters data174 includes EUV generation parameters and buffer flow parameters for alarge number of historical EUV generation processes. The contaminationdata 176 includes, for each historical EUV generation process, dataindicating the accumulation of droplet matter at various regions of thesurface 128 and the surface 130. As will be set forth in more detailbelow, the training module 170 utilizes the historical EUV systemparameters data 174 and the contamination data 176 to train the analysismodel 180 with a machine learning process.

In one embodiment, the historical EUV system parameters data 174includes data related to plasma generation parameters and buffer fluidflow parameters. The plasma generation parameters can include dropletspeed, droplet size, laser pulse energies, laser pulse timing, laserpulse location, 3D models of plasma generation, models of droplet shapeafter the first laser pulse and after the second laser pulse, and otherparameters related to the generation of EUV radiation forphotolithography processes. The buffer fluid flow parameters can includeflow rates from individual mass flow controllers, the flow rates fromthe outlet 112 or individual outlets 112, or other parameters related tothe flow of the buffer fluid 148.

In one embodiment, the contamination data 176 includes for eachhistorical EUV system parameters in the historical EUV system parametersdata 174, a respective label. Each label indicates the accumulation ofdroplet material at various regions of the surfaces 128 and 130.

In one embodiment the analysis model 180 includes a neural network.Training of the analysis model 180 will be described in relation to aneural network. However, other types of analysis models or algorithmscan be used without departing from the scope of the present disclosure.The training module 170 utilizes the training set data 172 to train theneural network with a machine learning process. During the trainingprocess, the neural network receives, as input, historical EUV systemparameters data 174 from the training set data 172. During the trainingprocess, the neural network outputs predicted contamination data. Thepredicted contamination data predicts, for each set of historical EUVsystem parameters provided to the analysis model 180, the contaminationmap corresponding to that set of data. The training process trains theneural network to generate predicted contamination data that matches thecontamination data 176 for each set of historical EUV system parameters.

In one embodiment, the neural network includes a plurality of neurallayers. The various neural layers include neurons that define one ormore internal functions. The internal functions are based on weightingvalues associated with neurons of each neural layer of the neuralnetwork. During training, the control system 134 compares, for each setof historical EUV system parameters data, the predicted contaminationdata to the actual label from the contamination data 176. The controlsystem generates an error function indicating how closely the predictedcontamination data matches the contamination data 176. The controlsystem 134 then adjusts the internal functions of the neural network.Because the neural network generates predicted contamination data basedon the internal functions, adjusting the internal functions will resultin the generation of different predicted contamination data for a sameset of historical EUV system parameters data. Adjusting the internalfunctions can result in predicted contamination data that produceslarger error functions (worse matching to the contamination data 176) orsmaller error functions (better matching to the contamination data 176).

After adjusting the internal functions of the neural network, thehistorical EUV system parameters data 174 is again passed to the neuralnetwork and the analysis model 180 again generates predictedcontamination data. The training module 170 again compares the predictedcontamination data to the contamination data 176. The training module170 again adjusts the internal functions of the neural network. Thisprocess is repeated in a very large number of iterations of monitoringthe error functions and adjusting the internal functions of the neuralnetwork until a set of internal functions is found that results inpredicted contamination data that matches the contamination data 176across the entire training set.

At the beginning of the training process, the predicted contaminationdata likely will not match the contamination data 176 very closely.However, as the training process proceeds through many iterations ofadjusting the internal functions of the neural network, the errorsfunctions will trend smaller and smaller until a set of internalfunctions is found that results in predicted contamination data thatmatch the contamination data 176. Matching can be based on a selectedthreshold. For example, the selected threshold error can be 5%. In thiscase, if the error is less than 5%, then the predicted contaminationdata is considered to match the contamination data 176. Identificationof a set of internal functions that results in predicted contaminationdata that matches the contamination data 176 corresponds to completionof the training process. Once the training process is complete, theneural network is ready to be used to adjust EUV generation parametersand buffer fluid flow parameters. In one embodiment, after the analysismodel 180 has been trained, the analysis model 180 can be utilized toanalyze the EUV generation parameters and the buffer fluid flowparameters and predict droplet accumulation of various regions of thesurfaces 128 and 130.

In one embodiment, the control system 134 includes processing resources182, memory resources 184, and communication resources 186. Theprocessing resources 182 can include one or more controllers orprocessors. The processing resources 182 are configured to executesoftware instructions, process data, make photolithography controldecisions, perform signal processing, read data from memory, write datato memory, and to perform other processing operations. The processingresources 182 can include physical processing resources 182 located at asite or facility of the EUV photolithography system. The processingresources can include virtual processing resources 182 remote from thesite EUV photolithography system or a facility at which the EUVphotolithography system is located. The processing resources 182 caninclude cloud-based processing resources including processors andservers accessed via one or more cloud computing platforms.

In one embodiment, the memory resources 184 can include one or morecomputer readable memories. The memory resources 184 are configured tostore software instructions associated with the function of the controlsystem and its components, including, but not limited to, the analysismodel 180. The memory resources 184 can store data associated with thefunction of the control system 134 and its components. The data caninclude the training set data 172, current process conditions data, andany other data associated with the operation of the control system 134or any of its components. The memory resources 184 can include physicalmemory resources located at the site or facility of the EUVphotolithography system 100. The memory resources can include virtualmemory resources located remotely from site or facility of the EUVphotolithography system 100. The memory resources 184 can includecloud-based memory resources accessed via one or more cloud computingplatforms.

In one embodiment, the communication resources can include resourcesthat enable the control system 134 to communicate with equipmentassociated with the EUV photolithography system 100. For example, thecommunication resources 186 can include wired and wireless communicationresources that enable the control system 134 to receive the sensor dataassociated with the EUV photolithography system and to control equipmentof the EUV photolithography system. The communication resources 186 canenable the control system 134 to control the various components of theEUV photolithography system. The communication resources 186 can enablethe control system 134 to communicate with remote systems. Thecommunication resources 186 can include, or can facilitate communicationvia, one or more networks such as wide networks, wireless networks, theInternet, or an intranet. The communication resources 186 can enablecomponents of the control system 134 to communicate with each other.

In one embodiment, the analysis model 180 is implemented via theprocessing resources 182, the memory resources 184, and thecommunication resources 186. The control system 134 can be a dispersedcontrol system with components and resources and locations remote fromeach other and from the EUV photolithography system.

The components, functionality, and processes described in relation tothe control system 134 and the analysis model 180 can be extended to thecontrol systems and analysis models described in relation to FIGS. 1-4.

FIG. 6 is a block diagram of an analysis model 180, according to oneembodiment. The analysis model 180 can be part of the control system 134of FIGS. 1A and 5 and can operate in conjunction with the systems andprocesses described in relation to FIGS. 1-6, according to oneembodiment. The analysis model 180 includes an encoder neural network190 and a decoder neural network 192. The analysis model 180 is trainedwith a machine learning process to identify recommended changes toplasma generation parameters based on sensed plasma and contaminationqualities, such as those sensed by the light sensors 162 and the chargedparticle detectors 160. The analysis model 180 of FIG. 6 is only oneexample of an analysis model. Many other kinds of analysis models andtraining processes can be utilized without departing from the presentdisclosure. The training process utilizes a training set. The trainingset includes historical plasma generation conditions data. Each set ofhistorical plasma generation conditions data includes, for a particularEUV generation process, the parameters of the flattening laser pulse,the parameters of the plasmatizing laser pulse, and the parameters ofthe droplets. The training set includes, for each set of historicalplasma generation conditions, historical contamination data thatresulted from the historical plasma generation conditions.

Each previously performed EUV generation process took place withparticular plasma generation conditions and resulted in particularcontamination patterns. The plasma generation conditions for each plasmadata value are formatted into a respective plasma generation conditionsvector 194. The plasma generation conditions vector 194 includes aplurality of data fields 166. Each data field 196 corresponds to aparticular process condition.

The example of FIG. 6 illustrates a single plasma generation conditionsvector 194 that will be passed to the encoder 190 of the analysis model180 during the training process. In the example of FIG. 6, the plasmageneration conditions vector 194 includes three data fields 166. A firstdata field 196 corresponds to the prepulse laser settings. In practice,there may be multiple data fields 166 for the prepulse laser settings,one for each of pulse power, pulse duration, pulse timing, etc. A seconddata field 196 corresponds to plasmatizing laser pulse settings. Inpractice, there may be multiple data fields 166 for each of a pluralityof settings include pulse power, pulse duration, pulse timing, and otherfactors. A third data field 196 corresponds to the droplet settings. Inpractice, there may be multiple data fields 166 for each of a pluralityof droplet settings including droplet speed, droplet size, droplettemperatures, etc. Each plasma generation conditions vector 194 caninclude different types of plasma generation conditions withoutdeparting from the scope of the present disclosure. The particularplasma generation conditions illustrated in FIG. 6 are given only by wayof example. Each process condition is represented by a numerical valuein the corresponding data field 196.

The encoder 190 includes a plurality of neural layers 198 a-c. Eachneural layer includes a plurality of nodes 200. Each node 200 can alsobe called a neuron. Each node 200 from the first neural layer 198 areceives the data values for each data field from the plasma generationconditions vector 194. Accordingly, in the example of FIG. 6, each node200 from the first neural layer 198 a receives three data values becausethe plasma generation conditions vector 194 has three data fields,though as mentioned above, in practice, the plasma generation conditionsvector 194 may include many more data fields than 3. Each neuron 200includes a respective internal mathematical function labeled F(x) inFIG. 6. Each node 200 of the first neural layer 198 a generates a scalarvalue by applying the internal mathematical function F(x) to the datavalues from the data fields 166 of the plasma generation conditionsvector 194. Further details regarding the internal mathematicalfunctions F(x) are provided below.

In the example of FIG. 6, each neural layer 198 a-168 e in both theencoder 190 and the decoder 192 are fully connected layers. This meansthat each neural layer has the same number of nodes as the succeedingneural layer. In the example of FIG. 6, each neural layer 198 a-168 eincludes five nodes. However, the neural layers of the encoder 190 andthe decoder 192 can include different numbers of layers than are shownin FIG. 6 without departing from the scope of the present disclosure.

Each node 200 of the second neural layer 198 b receives the scalarvalues generated by each node 200 of the first neural layer 198 a.Accordingly, in the example of FIG. 6 each node of the second neurallayer 198 b receives five scalar values because there are five nodes 200in the first neural layer 198 a. Each node 200 of the second neurallayer 198 b generates a scalar value by applying the respective internalmathematical function F(x) to the scalar values from the first neurallayer 198 a.

There may be one or more additional neural layers between the neurallayer 198 b and the neural layer 198 c. The final neural layer 198 c ofthe encoder 190 receives the five scalar values from the five nodes ofthe previous neural layer (not shown). The output of the final neurallayer is the predicted contamination data 202. In practice, thepredicted contamination data may be a vector including many data fields.Each data field corresponds to a particular aspect of a sensedcontamination map of the collector. The contamination map can indicatethe contamination level at each of a plurality of surface zones of thecollector. The contamination data vector includes data fields thatindicate the contamination level at the various surface zones.

During the machine learning process, the analysis model compares thepredicted contamination data 202 to the actual contamination data. Theanalysis model 180 generates an error value indicating the error ordifference between the predicted contamination data 202 The error valueis utilized to train the encoder 190.

The training of the encoder 190 can be more fully understood bydiscussing the internal mathematical functions F(x). While all of thenodes 200 are labeled with an internal mathematical function F(x), themathematical function F(x) of each node is unique. In one example, eachinternal mathematical function has the following form:

F(x)=x ₁ *w ₁ +x ₂ *w ₂ + . . . x _(n) *w ₁ +b.

In the equation above, each value x₁-x_(n) corresponds to a data valuereceived from a node 200 in the previous neural layer, or, in the caseof the first neural layer 198 a, each value x₁-x_(n) corresponds to arespective data value from the data fields 166 of the plasma generationconditions vector 194. Accordingly, n for a given node is equal to thenumber of nodes in the previous neural layer. The values w₁-w_(n) arescalar weighting values associated with a corresponding node from theprevious layer. The analysis model 180 selects the values of theweighting values w₁-w_(n). The constant b is a scalar biasing value andmay also be multiplied by a weighting value. The value generated by anode 200 is based on the weighting values w₁-w_(n). Accordingly, eachnode 200 has n weighting values w₁-w_(n). Though not shown above, eachfunction F(x) may also include an activation function. The sum set forthin the equation above is multiplied by the activation function. Examplesof activation functions can include rectified linear unit (ReLU)functions, sigmoid functions, hyperbolic tension functions, or othertypes of activation functions. Each function F(x) may also include atransfer function.

After the error value has been calculated, the analysis model 180adjusts the weighting values w₁-w_(n) for the various nodes 200 of thevarious neural layers 198 a-168 c. After the analysis model 180 adjuststhe weighting values w₁-w_(n), the analysis model 180 again provides theplasma generation conditions vector 194 to the input neural layer 198 a.Because the weighting values are different for the various nodes 200 ofthe analysis model 180, the predicted contamination data 202 will bedifferent than in the previous iteration. The analysis model 180 againgenerates an error value by comparing the actual contamination data tothe predicted contamination data 202.

The analysis model 180 again adjusts the weighting values w₁-w_(n)associated with the various nodes 200. The analysis model 180 againprocesses the plasma generation conditions vector 194 and generates apredicted contamination data 202 and associated error value. Thetraining process includes adjusting the weighting values w₁-w_(n) initerations until the error value is minimized.

FIG. 6 illustrates a single plasma generation conditions vector 194being passed to the encoder 190. In practice, the training processincludes passing a large number of plasma generation conditions vectors194 through the analysis model 180, generating a predicted contaminationdata 202 for each plasma generation conditions vector 194, andgenerating an associated error value for each predicted contaminationdata. The training process can also include generating an aggregatederror value indicating the average error for all the predictedcontamination data for a batch of plasma generation conditions vectors194. The analysis model 180 adjusts the weighting values w₁-w_(n) afterprocessing each batch of plasma generation conditions vectors 194. Thetraining process continues until the average error across all plasmageneration conditions vectors 194 is less than a selected thresholdtolerance. When the average error is less than the selected thresholdtolerance, the training of the encoder 190 is complete and the analysismodel is trained to accurately predict the contamination data based onthe plasma generation conditions.

The decoder 192 operates and is trained in a similar manner as theencoder 190 as described above. During the training process of thedecoder 192, the decoder receives contamination data associated with aplasma generation conditions vector 194. The contamination data isreceived by each node 200 of the first neural layer 198 d of the decoder192. The nodes 200 and the first neural layer 198 d apply theirrespective functions F(x) to the contamination data values and pass theresulting scalar values to the nodes 200 of the next neural layer 198 e.After the final neural layer 198 f processes the scalar values receivedfrom the previous neural layer (not shown), the final neural layer 198 foutputs a predicted plasma generation conditions vector 204. Thepredicted plasma generation conditions vector 204 has the same form asthe plasma generation conditions vector 194. The data fields 205 of thepredicted plasma generation conditions vector 204 represent the sameparameters or conditions as the data fields 196 of the plasma generationconditions vector 194.

The training process compares the predicted plasma generation conditionsvector 204 to the plasma generation conditions vector 194 and determinesan error value. The weighting parameters of the functions F(x) of thenodes 200 of the decoder 192 are adjusted and the contamination data isagain provided to the decoder 192. The decoder 192 again generates apredicted plasma generation conditions vector 204 and an error value isdetermined. This process is repeated for all of the plasma generationconditions vectors in the historical plasma generation conditions dataand for all of the historical contamination data from the historicalplasma data until the decoder 192 can generate, for each historicalplasma data value, a predicted plasma generation conditions vector 172that matches the corresponding plasma generation conditions vector 194.The training process is complete when a prediction cumulative errorvalue is lower than the threshold error value.

After the encoder 190 and the decoder 192 have been trained as describedabove, the analysis model 180 is ready to generate recommended plasmageneration parameters to reduce contamination, and hence, the resultingEUV quality produced by the EUV photolithography systems described inrelation to FIGS. 1-5. During operation, the analysis model receives acurrent plasma generation conditions vector representing currentconditions or parameters of the EUV photolithography systems describedin relation to FIGS. 1-5. The encoder 190 processes the current plasmageneration conditions vector and generates predicted futurecontamination data based on the current plasma generation conditionsvector. If the predicted future contamination data is less than desired,then the decoder 192 is utilized to generate a set of recommended plasmageneration conditions that will result in reduced contamination. Inparticular, the decoder 192 receives contamination data reflectingreduced contamination. The decoder 192 then generates a predicted plasmageneration conditions vector based on the reduced contamination values.

The predicted plasma generation conditions vector includes recommendedplasma generation conditions values for certain of the plasma generationconditions types. For example, the predicted plasma generationconditions vector can include a recommended values for the variousprepulse laser conditions, the plasmatizing laser pulse conditions, andthe droplet conditions. These conditions can include laser prepulse andplasma pulse energy, laser position, laser stability, beam size, pulseduration, laser wavelength, laser pulse timing, droplet position,droplet stability, droplet timing, plasma ion density, plasma electrondensity, plasma temperature, plasma pancake angle, and plasma position.

Many other kinds of analysis models, training processes, and data formscan be utilized without departing from the scope of the presentdisclosure.

In another example, the contamination data 202 includes plasma qualitydata. In other words, the output of the encoder includes contaminationdata and plasma quality data. In this case, the training processincludes not only historical contamination data, but also historicalplasma quality data. The historical plasma quality data corresponds tocharacteristics of the plasmatized droplets that resulted fromparticular historical plasma generation conditions. The historicalplasma quality can determined based on the output of the light sensors162 and the charged particle detectors 160 as described previously. Thetraining process trains the encoder 190 to predict both contaminationdata and plasma quality data based on the plasma generation conditionsvectors 194. The decoder 192, in turn, is trained to predict plasmageneration conditions that result in the plasma quality data and thecontamination data. This results in the decoder 192 being able togenerate recommended plasma generation conditions that will result inboth improved contamination data and improved/maintained plasma quality.

In another example, the plasma generation conditions vectors 194 caninclude buffer fluid flow parameters. The buffer fluid flow parameterscan indicate the flow rate of buffer fluid through various channels, aswell as the position of director vanes. In this case, the analysis model180 can be trained to suggest buffer fluid flow parameters that willresult in reduced contamination using the same training principlesdescribed above but including buffer fluid flow data in the plasmaconditions vectors 194. FIG. 7 is a flow diagram of a method 700 foroperating a photolithography system, according to one embodiment. Themethod 700 can utilize the systems, components, and processes describedin relation to FIGS. 1-6. At 702, the method 700 includes detecting adrop in reflectivity of a collector mirror. One example of a collectormirror is the collector mirror 102 of FIG. 1A. At 704, the method 700includes analyzing a contamination image of the reflector mirror. At706, the method 700 includes adjusting plasma generation conditions. At708, the method 700 includes calculating buffer fluid flow conditionsfor reducing contamination. At 710, the method 700 incudes adjustingbuffer fluid flow parameters.

FIG. 8 is a method 800 for operating a photolithography system,according to one embodiment. The method 800 can utilize the systems,components, and processes described in relation to FIGS. 1-7. At 802,the method 800 includes monitoring a contamination image of a collectormirror. One example of a collector mirror is the collector mirror 102 ofFIG. 1A. At 804, the method 800 includes providing the contaminationimage to an analysis model. One example of an analysis model is theanalysis model 180 of FIG. 5. At 806, the method 800 includes predictinga contamination image at a future time period with the analysis modelbased on current EUV generation parameters. At 808, the method 800includes generating, with the analysis model, new EUV generationparameters for reducing contamination. At 810, the method 800 includesimplementing the new EUV generation parameters.

FIG. 9 is a method 900 for reducing contamination in an EUVphotolithography system, according to an embodiment. The method 900 canutilize the systems, components, and processes described in relation toFIGS. 1-8. At 902, the method 900 includes performing a photolithographyprocess by generating extreme ultraviolet radiation in an extremeultraviolet radiation generation chamber. One example of an extremeultraviolet radiation generation chamber is the extreme ultravioletgeneration chamber 101 of FIG. 1A. At 904, the method 900 includesflowing a buffer fluid into the extreme ultraviolet radiation generationchamber. At 906, the method 900 includes generating sensor signalsindicative of contamination of the collector mirror in the extremeultraviolet radiation generation chamber. One example of a collectormirror is the collector mirror 102 of FIG. 1A. At 908, the method 900includes adjusting a flow of the buffer fluid into the extremeultraviolet radiation generation chamber based on analysis of the sensorsignals by the analysis model trained with a machine learning process.One example of an analysis model is the analysis model 180 of FIG. 5.

FIG. 10 is a method 1000 for reducing contamination in an EUVphotolithography system, according to one embodiment. The method 1000can utilize the systems, components, and processes described in relationto FIGS. 1-9. At 1002, the method 1000 includes outputting a stream ofdroplets from a droplet generator. One example of droplets are thedroplets 140 of FIG. 1B. One example of a droplet generator is thedroplet generator 114 of FIG. 1B. At 1004, the method 1000 includesgenerating, in an extreme ultraviolet radiation generation chamber, aplasma by irradiating the droplets with a laser. One example of anextreme ultraviolet radiation generation chamber is the extremeultraviolet radiation generation chamber 101 of FIG. 1B. One example ofa laser is the laser 106 of FIG. 1B. At 1006, the method 1000 includesreflecting the extreme ultraviolet radiation with a collector mirror.One example of the collector mirror is the collector mirror 102 of FIG.1B. At 1008, the method 1000 includes receiving a buffer fluid into afluid distributor via a plurality of mass flow controllers each coupledto a respective inlet of the fluid distributor. One example of a fluiddistributor is the fluid distributor 108 of FIG. 1B. One example of massflow controllers are the mass flow controllers 1020 of FIG. 1B. Oneexample of an inlet is the inlets 110 of FIG. 1B. At 1010, the method1000 includes flowing the buffer fluid into the extreme ultravioletradiation generation chamber from the fluid distributor.

In one embodiment, a photolithography system includes a shield includingan interior surface and a collector mirror coupled to the shield andincluding a reflective surface. The collector mirror and the shielddefine an extreme ultraviolet radiation generation chamber. The systemincludes a fluid source configured to hold a buffer fluid, a pluralityof mass flow controllers each configured to receive the buffer fluidfrom the fluid source, and a fluid distributor. The fluid distributorincludes a plurality of fluid inlets each coupled to a respective one ofthe mass flow controllers and configured to receive the buffer fluidfrom the mass flow controller and one or more outlets configured tosupply the buffer fluid into the extreme ultraviolet radiationgeneration chamber.

In one embodiment, a method includes performing a photolithographyprocess by generating extreme ultraviolet radiation in an extremeultraviolet radiation generation chamber and flowing a buffer fluid intothe extreme ultraviolet radiation generation chamber. The methodincludes generating sensor signals indicative of contamination of acollector mirror in the extreme ultraviolet radiation generationchamber. The method includes adjusting flow of the buffer fluid into theextreme ultraviolet radiation generation chamber based on analysis ofthe sensor signals by an analysis model trained with a machine learningprocess.

In one embodiment, a method includes outputting a stream of dropletsfrom a droplet generator and generating, in an extreme ultravioletradiation generation chamber, a plasma by irradiating the droplets witha laser. The method includes reflecting the extreme ultravioletradiation with a collector mirror, receiving a buffer fluid into a fluiddistributor via a plurality of mass flow controllers each coupled to arespective inlet of the fluid distributor, and flowing the buffer fluidinto the extreme ultraviolet radiation generation chamber from the fluiddistributor.

Embodiments of the present disclosure provide many benefits to extremeultraviolet radiation photolithography systems. Embodiments of thepresent disclosure reduce contamination of components of the extremeultraviolet photolithography systems. Embodiments of the presentdisclosure dynamically adjust the flow of a buffer fluid into an extremeultraviolet radiation generation chamber. The buffer fluid helps toprevent and remove contamination of sensitive components of the extremeultraviolet radiation generation chamber. This helps to ensure thatphotolithography processes have adequate extreme ultraviolet radiation.Furthermore, because contamination is removed and prevented, sensitivecomponents of the extreme ultraviolet radiation systems do not have tobe replaced as frequently. The sensitive components can be extremelyexpensive. Accordingly embodiments of the present disclosure not onlyenhance the effectiveness of photolithography processes, but they alsoreduce the cost of operating the photolithography system becausecomponents need to be replaced less frequently.

The various embodiments described above can be combined to providefurther embodiments. Aspects of the embodiments can be modified, ifnecessary, to employ concepts of the various patents, applications andpublications to provide yet further embodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

1. A photolithography system, comprising: a shield including an interiorsurface; a collector mirror coupled to the shield and including areflective surface (128), wherein the collector mirror and the shielddefine an extreme ultraviolet radiation generation chamber; a fluidsource configured to hold a buffer fluid; a plurality of mass flowcontrollers each configured to receive the buffer fluid from the fluidsource; and a fluid distributor including: a plurality of fluid inletseach coupled to a respective one of the mass flow controllers andconfigured to receive the buffer fluid from the mass flow controller;and one or more outlets configured to supply the buffer fluid into theextreme ultraviolet radiation generation chamber.
 2. Thephotolithography system of claim 1, wherein the fluid distributorincludes a fluid chamber communicably coupled between the fluid inletsand the fluid outlet.
 3. The photolithography system of claim 1, whereinthe fluid distributor includes a plurality of outlets and a plurality offluid chambers separated from each other and each coupling a respectiveone of the inlets to a respective one of the outlets.
 4. Thephotolithography system of claim 3, further comprising a plurality ofadjustable director vanes each positioned adjacent to a respectiveoutlet and configured to direct a first portion of the buffer fluidtoward the collector mirror and to direct a second portion of the bufferfluid toward the interior surface of the shield.
 5. The photolithographysystem of claim 1, wherein the fluid distributor includes: a first fluidchamber configured to receive the buffer fluid from a first group of theinlets; a first outlet configured to supply the buffer fluid from thefirst fluid chamber into the extreme ultraviolet radiation generationchamber; a second fluid chamber configured to receive the buffer fluidfrom a second group of the inlets; and a second outlet configured tosupply the buffer fluid from the second fluid chamber into the extremeultraviolet radiation generation chamber.
 6. The photolithography systemof claim 5, wherein the first fluid chamber is coaxial with the secondfluid chamber.
 7. The photolithography system of claim 1, wherein themass flow controllers are each positioned in the respective inlet. 8.The photolithography system of claim 1, further comprising: one or moresensors configured to output sensor signals indicative of contaminationof the reflective surface of the collector mirror; and a control systemconfigured to receive the sensor signals and to adjust flow of thebuffer fluid into the extreme ultraviolet radiation generation chamberresponsive to the sensor signals.
 9. The photolithography system ofclaim 8, wherein the control system includes an analysis model trainedwith a machine learning process to select buffer fluid flow parametersresponsive to contamination of the reflective surface of the collectormirror.
 10. The photolithography system of claim 9, wherein the analysismodel includes a neural network.
 11. A method, comprising: performing aphotolithography process by generating extreme ultraviolet radiation inan extreme ultraviolet radiation generation chamber; flowing a bufferfluid into the extreme ultraviolet radiation generation chamber;generating sensor signals indicative of contamination of a collectormirror in the extreme ultraviolet radiation generation chamber; andadjusting flow of the buffer fluid into the extreme ultravioletradiation generation chamber based on analysis of the sensor signals byan analysis model trained with a machine learning process.
 12. Themethod of claim 11, wherein adjusting flow of the buffer fluid includesselectively adjusting a flow rate of the buffer fluid from multiple massflow controllers.
 13. The method of claim 11, wherein adjusting flow ofthe buffer fluid includes adjusting a director vane positioned at anoutlet of a fluid dispenser that outputs the buffer fluid into theextreme ultraviolet radiation generation chamber.
 14. The method ofclaim 11, wherein the buffer fluid is configured to remove accumulationof debris from the collector mirror.
 15. The method of claim 11, furthercomprising: generating a contamination map of the collector mirror basedon the sensor signals; and selecting buffer fluid flow parameters withthe analysis model to reduce contamination of the collector mirror basedon the contamination map.
 16. The method of claim 11, wherein thecontamination results from irradiating droplets with laser light withinthe extreme ultraviolet radiation generation chamber, wherein the bufferfluid is selected to etch material from the droplets.
 17. The method ofclaim 16, wherein the droplets include tin, wherein the buffer fluidincludes hydrogen gas.
 18. A method, comprising: outputting a stream ofdroplets from a droplet generator; generating, in an extreme ultravioletradiation generation chamber, a plasma by irradiating the droplets witha laser; reflecting the extreme ultraviolet radiation with a collectormirror; receiving a buffer fluid into a fluid distributor via aplurality of mass flow controllers each coupled to a respective inlet ofthe fluid distributor; and flowing the buffer fluid into the extremeultraviolet radiation generation chamber from the fluid distributor. 19.The method of claim 18, further comprising: sensing contamination of thecollector mirror with one or more sensors; and selecting, with ananalysis model, new extreme ultraviolet radiation generation parametersand new buffer fluid flow parameters based on the contamination of thecollector mirror; and reducing the contamination of the collector mirrorby implementing the new extreme ultraviolet radiation generationparameters and the new buffer fluid flow parameters.
 20. The method ofclaim 19, further comprising training the analysis model with a machinelearning process to select new extreme ultraviolet radiation generationparameters and new buffer fluid flow parameters based on thecontamination of the collector mirror.